What was the holocaust by bullets?

What was the Holocaust by Bullets, as explained on the website yahadinunum.org – the work of Father Desbois and the video? What did you learn from the witness testimony? Click on the following link:

https://www.ushmm.org/information/exhibitions/online-exhibitions/special-focus/desbois

https://www.yahadinunum.org/guide-to-the-holocaust-by-bullets 

https://www.yahadinunum.org/en/holocaust-by-bullets

https://yahadmap.org/#map/

Click on by Country. Go to the country map, pick a country, and write about what you learned about the Nazi killings in that country. What were the “Einsatzgruppen” (incorporate article “Bringing Death to Jews” from the Hayes e-book, and material from the yahadinunum website)? You can answer each question separately.